The process of discovering new drugs for treatment of medical disorders often requires administering hundreds of test compounds to human volunteers. If the test compound relieves the manifestations of the disorder, it is considered to be a candidate drug and subjected to further testing.
For many disorders, the manifestations of the disorder are readily observable. However, in the case of neurological disorders, the manifestations are more difficult to quantify. For example, if one were to give a test compound to a volunteer afflicted with Alzheimer's, one would want to test the effect on that volunteer's short term memory. Each such test is a time-consuming proposition. Adding to this difficulty is the need to test enough volunteers to ensure that the conclusions drawn from these tests merit statistical significance.
Other neurological disorders, for example epilepsy, are characterized by transient episodes. The search for drugs having therapeutic value in treatment of epilepsy thus requires long periods of time during which one must somehow monitor the frequency, duration, and severity of seizures. The search for drugs effective in suppressing symptoms of schizophrenia requires somehow determining the extent to which a volunteer's perception of reality differs from reality, a measure that is fraught with subjective uncertainties.